1. Field of the Invention
The present invention relates to an IP multicasting system, and more specifically, to a satellite IP multicasting system wherein satellite multicasting network is used to bypass backbone network of ISP and satellite network is interworked directly to local node of ISP, and method for constructing an IP multicast network by a unit of local node of ISP, that is, or by a unit of internet node having a router for subscriber connection and a switch, and for transmitting a multicasting packet transmitted from a content provider into a local IP multicast network via a satellite, and method for interworking satellite multicasting network and local access network.
2. Description of the Prior Art
In comparison with multicasting protocol, unicasting protocol is inefficient in terms of network traffic and transmission cost because the same data packet is replicated at a source server and is sent respectively to each subscriber who is connected to the source server, which causes network traffic in proportion to the number of concurrent connectors.
Despite the merit of IP multicasting protocol, it is very difficult to embody the solution on the whole internet network due to the network complexity of backbone network and possibility and impact of anomaly during new configuration process.
As shown in FIG. 1, a solution used in current internet broadcasting generally uses a unicasting system wherein a server of an internet broadcasting station exchanges data with a viewer. However, simultaneous connectors should share limited capacity of transmission network between the internet broadcasting station and connectors in the unicasting system.
Suppose that an internet broadcasting provider provides internet broadcasting service via a transmission network of 155 Mbps at a transmission speed of 512K, In this case, when simultaneous connectors are over 300, capacity of transmission network reaches the limit.
If the connectors exceed 300, the screen display is stopped or picture quality is degraded. As a result, a user cannot watch a normal screen.
Referring to FIG. 1, in the Contents Provider (hereinafter, referred to as “CP”) such as an internet broadcasting provider, a management server 14 and a media server 12 are connected to a router 10 constituting main nodes. The router 10 is connected to a router 22 of a backbone network 20. The other terminal router 24 of the backbone network 20 is connected to a router 30 constituting networks of corporations or PC bang.
When the CP provides motion picture transmission service of 512 Kbps, and 15 subscribers 32 simultaneously connects with this service, a media server (main server) of the CP in unicasting protocol should transmit data to 15 clients 32, respectively. As a result, actually required capacity of transmission network is 7.680 Mbps (512 Kbps×15) in proportion to data to be transmitted and the number of simultaneous connectors.
The CP should secure a band of bottleneck interval (between the router 10 and the router 22 of the backbone network 20) so that simultaneous connectors may receive the service without delay. However, since it costs a great deal for security of sufficient band, the CP cannot but limit the number of simultaneous connectors or the content transmission speed.
In case of the band of bottleneck interval secured as 8 Mbps, if the number of simultaneous connectors exceeds 15, a required band exceeds 8 Mbps. As a result, a user cannot receive the normal motion picture service.
When contents such as internet broadcasting are provided with the unicast system, channels cannot be effectively used due to bottleneck phenomenon of network. The bottleneck phenomenon also causes the increase in CPU load of the media server 12 or the routers 10 and 22 of the CP for duplicating data as many as the number of clients. As a result, the unicast system is not suitable when the internet broadcasting has a lot of clients.
The security of required transmission band, the limit of subscribers and the enlargement of server capacity mainly degrade profitability of content providers. When subscribers of more than the transmission band are allowed for improvement of profitability, transmission delay occurs so that service of good quality cannot be provided. Additionally, the CP should reduce the amount of content data to attract subscribers as many as possible in a limited transmission line. As a result, the quality of image is degraded, and improvement of contents and internet broadcasting business is prevented.
In order to solve the problem of the unicast system, a content delivery network (hereinafter, referred to as “CDN”) solution is suggested.
The CDN comprises streaming servers 26 individually disposed in various local nodes 28 of a backbone network 20 other than a media server (main server) 12 of a CP. The CDN provides contents from the most adjacent local node to a user by previously mirroring main contents to the streaming server 26 of the local node 28. The CDN reduces a system (server, switch, router) path which a subscriber connects with and pass through, thereby decreasing transmission delay resulting from network traffic and distributing load of the media server 12 of the CP to simultaneous connection of subscribers. As a result, the quality of service to transmission speed and transmission delay is more or less improved.
If a user connects with a management server 14 of the CP hosting in the CDN to select motion picture watching, the management server 14 of the CP transmits a URL (uniform resource locator) of corresponding contents in the main node management system (not shown) into the user, and the user requires the corresponding contents to the main node management system of the CDN with the transmitted URL.
The main node management system of the CDN detects location of a user to transmit a URL of the optimum local node router 24. If the user request contents to the local node router 24 corresponding to the URL transmitted from the CDN management system, the streaming server 26 of the local node router 24 transmits motion images into the user that requests the contents.
However, the above-described CDN has not solved the problems of unicast transmission systems. Although the media server 12 of the CP may load traffic to push multimedia contents into local nodes (e.g. 11 local nodes) using a leased channel, connectors should share the limited line capacity of networks from the streaming server 26 of the local node router 24 to subscribers like the above-mentioned problem of the unicast transmission system of FIG. 1.
Additionally, in proportion to the transmission speed and the number of simultaneous connectors, the transmission band required between the main server and various local node streaming servers should be hired from internal service providers or CDN providers.
In spite of the above-described problems such as traffic of network in the conventional unicast transmission system and the CDN solution, the limitation in the number of simultaneous connectors and the cost resulting from enlargement of capacity of leased channels, to embody an IP multicasting solution on the whole internet network is difficult in aspects of technology, time and cost.
As a result, it is difficult to smoothly provide content service for internal broadcasting or internet in education wherein multiple access is performed via the conventional internet network.